In the field of wall covering materials to afford comforts and/or decorative effects to the interior of cars, ships or buildings, a corrugated paperboard has recently attracted increasing attention as a basic material because of its light weight, low cost, good heat and sound insulating ability and fairly good adaptability to various mechanical processings. A variety of materials such as wood pulp, cotton, flax and felt are used as the paperboard. In automobiles, for example, trim boards such as a roof trim boards of corrugated paperboard base have already been in practical use on an industrial scale. The trim boards of this type usually consist of a substrate of corrugated paperboard and a facing layer such as polyvinyl chloride sheet which is laid on one side of the corrugated paperboard for producing protective, decorative and/or cushioning effects. In most cases, the corrugated paperboard substrate takes the form of a double-faced board given by bonding liners to both sides of a corrugated medium using a thermoplastic resin as the adhesive. Since walls (including ceiling of the automobile) to be covered by the trim boards usually have curved surfaces, the trim boards are produced as at least partly curved boards in conformance with the curved wall surfaces. Press-forming with application of heat is usually used for producing the curved trim boards of corrugated paperboard base. In most cases, the corrugated paperboard alone is formed into a desired shape by means of a hot-press, followed by the application of the facing layer onto the shaped corrugated substrate with the interposal of a hot-melt type adhesive layer and followed by the application of another hot-press to accomplish the bonding between the shaped corrugated paperboard and the facing layer.
In case of setting the facing layer on or over the shaped corrugated paperboard in the hot-press machine, the facing layer should be stationarily held by some holding means to allow the facing layer to be radially outwardly stretched under pressing of the facing layer against the shaped corrugated paperboard in order to avoid undesired wrinkles in the curved areas of the bonded facing layer.
Hitherto, such setting of the facing layer has been made by at least two workers who stand beside the hotpress machine, gripping and pulling the corners of the facing layer radially outwardly. However, it is clear such manual procedure is troublesome thus decreasing the trim board production efficiency of the hot-press machine.